1. Field of the Invention
The present invention relates to an overshoot/undershoot prevention device and overshoot/undershoot prevention method for outputting a received waveform signal as a regulated waveform with attenuated overshoot and undershoot.
2. Description of the Related Art
Japanese Patent Laid-open No. 291931/93 discloses one example of this type of device in the prior art. The invention disclosed in the above official gazette is directed to solving a problem that a high level of overshoot, undershoot, or ringing occurs in an open-drain output circuit of the prior art. This problem arises when the input voltage changes from High level to Low level, whereupon the resistance across the source and drain of the output transistor is low and considerable time is required until the discharged energy attenuates. According to the construction of this invention, the device is provided with:
a package having a reference region in at least one portion;
an output terminal provided in the package that is connected to an outside power source by way of a load resistance;
a common terminal provided in the package that is connected to an external reference potential point and that generates a load capacitance between the load resistance;
a field effect transistor provided on the package having its drain region connected to the output terminal and its source region connected to a common terminal and in which conductivity between the drain region and source region changes in accordance with the value of a control voltage applied between the gate region and source region; and
a control voltage generating means that, when changing the control voltage from a high level to a low level when the input voltage makes a stepped change from a high level to a low level, effects a two-stage change from a high rate of change per unit time to a low rate of change per unit time.
In the device disclosed in Japanese Patent Laid-open No. 291931/93 configured as described above, when the control voltage generated by the control voltage generating means changes from High level to Low level, the rate of change per unit time changes from a high rate to a low rate, and the resistance across the drain region and source region of the field effect transistor therefore quickly rises to a particular value and then increases gradually. The resistance across the drain region and source region of the field effect transistor is therefore held at an intermediate value between the ON resistance and OFF resistance longer than in a device of the prior art, and the attenuation of the discharge energy is thus effected more rapidly.
Although the above-described prior art regulates attenuation by controlling resistance value, no particular consideration is given to the characteristics when actually connected to a transmission line. When actually connected to a transmission line, the problem typically occurs that a circuit having superior overshoot suppressing characteristics exhibits weak undershoot suppressing characteristics, and a circuit having superior undershoot suppressing characteristics exhibits weak overshoot suppressing characteristics.
The present invention was achieved in view of the above-described problems and has the object of providing an overshoot/undershoot prevention device and overshoot/undershoot prevention method that feature both good overshoot and undershoot characteristics when connected to a transmission line.
The overshoot/undershoot prevention device of the present invention attenuates overshoot and undershoot from a waveform signal that is applied to a waveform input section and outputs the result as a shaped waveform, the device includes an overshoot shaping device that attenuates overshoot from the waveform signal and outputs the result as a shaped waveform, and an undershoot shaping device that attenuates undershoot from the waveform signal and outputs the result as the shaped waveform;
wherein the overshoot shaping device selects the portion of the waveform signal that equals or exceeds an overshoot determining potential when the potential of the waveform signal equals or exceeds the overshoot determining potential and outputs the selected portion as an overshoot waveform, attenuates the overshoot component of that waveform signal according to the time the overshoot waveform continues, and outputs the result as the shaped waveform; and
the undershoot shaping device selects the portion of the waveform signal that equals or falls below an undershoot determining potential when the potential of the waveform signal equals or falls below the undershoot determining potential and outputs the selected portion as an undershoot waveform, attenuates the undershoot component of that waveform signal according to the time that the undershoot waveform continues, and outputs the result as the shaped waveform.
In this case, the overshoot shaping device may be provided with:
an overshoot determining means that compares the overshoot determining potential received from an overshoot determining potential input section with the potential of the waveform signal applied to the waveform input section, selects the portion of the waveform signal that equals or exceeds the overshoot determining potential when the potential of the waveform signal equals or exceeds the overshoot determining potential and outputs the selected portion as an overshoot waveform;
an overshoot time detecting means that takes in the overshoot waveform to find the time that the overshoot waveform continues and outputs an overshoot time signal; and
an overshoot attenuation outputting means that, in addition to taking in the waveform signal and the overshoot time signal, attenuates the overshoot component of the waveform signal according to the time the overshoot waveform continues based on the overshoot time signal and outputs the result as the shaped waveform.
Further, the undershoot shaping device may be provided with:
an undershoot determining means that compares the undershoot determining potential received from an undershoot determining potential input section with the potential of the waveform signal applied to the waveform input section, selects the portion of the waveform signal that equals or falls below the undershoot determining potential when the potential of the waveform signal equals or falls below the undershoot determining potential, and outputs the selected portion as an undershoot waveform;
an undershoot time detecting means that takes in the undershoot waveform to find the time that the undershoot waveform continues, and outputs an undershoot time signal; and
an undershoot attenuation outputting means that, in addition to taking in the waveform signal and the undershoot time signal, attenuates the undershoot component of the waveform signal according to the time that the undershoot waveform continues based on the undershoot time signal, and outputs the result as the shaped waveform.
In addition, the overshoot determining means may also include: a first differential circuit that compares the overshoot determining potential received from the overshoot determining potential input section with the potential of the waveform signal applied to the waveform signal input section, selects the portion of the waveform signal that equals or exceeds the overshoot determining potential when the potential of the waveform signal equals or exceeds the overshoot determining potential, and outputs the selected portion as the overshoot waveform.
The overshoot time detecting means may include a differentiating circuit that is provided with a first capacitance member and a second resistance member and that differentiates the overshoot waveform and outputs the obtained differentiated waveform as the overshoot time signal.
The overshoot attenuation outputting means may include:
a first resistance member that is connected to the overshoot attenuating potential; and
an NMOS transistor that, in addition to taking in the waveform signal and the overshoot time signal, is activated in accordance with the time that the overshoot waveform continues based on the overshoot time signal, attenuates the overshoot component of the waveform signal via the first resistance member, and outputs the result as the shaped waveform.
The undershoot determining means may include a second differential circuit that compares the undershoot determining potential received from the undershoot determining potential input section with the potential of the waveform signal that is applied to the waveform input section, selects the portion of the waveform signal that equals or falls below the undershoot determining potential when the potential of the waveform signals equals or falls below the undershoot determining potential, and outputs the selected portion as the undershoot waveform.
The undershoot time detecting means may include a differentiating circuit that is provided with a second capacitance member and a fourth resistance member, and that differentiates the undershoot waveform and outputs the obtained differentiated waveform as the undershoot time signal.
The undershoot attenuation output means may include:
a third resistance member that is connected to the undershoot attenuating potential; and
a PMOS transistor that, in addition to taking in the waveform signal and the undershoot time signals, is activated in accordance with the time that the undershoot waveform continues based on the undershoot time signals, attenuates the undershoot component of the waveform signal via the third resistance member, and outputs the result as the shaped waveform.
The overshoot/undershoot prevention method of the present invention attenuates overshoot and undershoot from a waveform signal that is applied to a waveform input section and outputs the result as a shaped waveform, the method includes:
an overshoot shaping process in which overshoot is attenuated from the waveform signal and the result outputted as a shaped waveform, and an undershoot shaping process in which undershoot is attenuated from the waveform signal and the result outputted as the shaped waveform;
wherein the overshoot shaping process is a process in which the portion of the waveform signal that equals or exceeds an overshoot determining potential is selected when the potential of the waveform signal equals or exceeds the overshoot determining potential and is outputted as an overshoot waveform, and the overshoot component of the waveform signal is attenuated and outputted as the shaped waveform in accordance with the time that the overshoot waveform continues; and
the undershoot shaping process is a process in which the portion of the waveform signal that equals or falls below an undershoot determining potential is selected and outputted as an undershoot waveform when the potential of the waveform signal equals or falls below the undershoot determining potential, and the undershoot component of the waveform signal is attenuated and outputted as the shaped waveform in accordance with the time that the undershoot waveform continues.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.